A technology is proposed to extract a face image which is not influenced by disturbance light (for example, refer to Patent Document 1). A difference image is obtained from a bright capture image, which is captured with a light source lighted up, and a dark capture image, which is captured without a light source lighted up. If a person is present, a face mask of the person is generated and the background is removed. A face image is thereby extracted from the difference image.                Patent Document 1: JP 2007-25758 A        
If a face image from which an influence of disturbance light is removed is used to detect sleepiness or drowsiness of a driver, an environment of an outside of the vehicle cannot be grasped from the face image. When the driver narrows his/her eyes, it may be therefore difficult to determine whether narrowing the eyes is caused by the sunlight incident or the sleepiness.